Air divider ring structure for jet engine inlet air duct

ABSTRACT

One or more inlet air dividing, sound absorptive rings are supported co-axially within the inlet duct of a jet engine nacelle on a plurality of radially inwardly extending, streamlined struts. In one form of the invention, these struts are telescopically extensible and retractable to move the rings from deployed position concentrically in the air duct to stowed condition within the cowl defining the air duct. In the other forms of the invention each sound absorptive ring comprises a plurality of arcuate acoustical honeycomb panel sections releasably connected at their lateral edges by piano hinge type connectors to narrow longerons supported by said struts, the panel sections and the longerons comprising complementary segments of each sound absorptive ring.

United States Patent Eschenburg 1451 May 30,1972

. [54] AIR DIVIDER RING STRUCTURE FOR JET ENGINE INLET AIR DUCT [7 2]Inventor: Rodney Eschenburg, San Diego, Calif. [73] Assignee: RohrCorporation 22 Filed: Nov. 12, 1970 [21] App]. No.: 88,542

FOREIGN PATENTS OR APPLICATIONS 935,119 8/1963 Great Britain ..l81/33.2l

Primary Examiner-Clarence R. Gordon At10rneyGeorge E. Pearson [5 7]ABSTRACT One or more inlet air dividing, sound absorptive rings are sup-52 us. (:1 ..1s1 33 HA,415 /119 Ported waxially within the inlet due: ofa jet engine nacelle [51] Int. Cl. ..Gl0k 11/04 on a plurality ofradially inwardly Extending Streamlined [58] Field of Search ..60/269,226; 181/3321; Struts. n one form of the i n n, these struts r l opi-415/1 19 cally extensible and retractable to move the rings fromdeployed position concentrically in the air duct to stowed con-References Cited dition within the cow] defining the air duct. In theother forms UNITED STATES PATENTS of the invention each sound absorptivering comprises a plurallty of arcuate acoust1cal honeycomb panelsections 3,481,427 12/1969 Dobbs ..415/ l 19 releasably connected attheir lateral edges by piano hinge type 3,477,231 11/1969 PaulSOnconnectors to narrow longerons supported by said struts, the 2,369,6701/1959 Hoffman-H 35 panel sections and the longerons comprisingcomplementary 3,303,653 2/1967 Hull .60/226 A segments f a h soundabsorptive ring. 3,346,174 10/1967 Lievens ..4l5/l19 3,508,838 4/1970Martenson ..4l5/1 19 4 Claims, 9 Drawing Figures so es 64 -a 83 92TTTCII 84 50'\ 53 9| 8 67 fa 1; sz 53 -9s -1 -::.:i;- a

Patented May 30, 1972 4 Sheets-Sheet 1 INVENTOR- RODNEY ESCHENBURGATTORNEY Patented May 30, 1972 3,666,043

4 Sheets-Sheet 2 I 27 23 23 INVENTOR.

RODNEY ESCHENBURG .4 BY FIG 3.6mm

ATTORNEY AIR DIVIDER RING STRUCTURE FOR JET ENGINE INLET AIR DUCTBACKGROUND OF THE INVENTION In recent years, the problem of suppressingjet engine noise has been a matter of extreme and increasing urgency.Legislation is now in effect aimed at reducing such noise, and strongforces are working toward even more stringent suppressive measures.

Two principal zones of a jet engine are responsible for most of theobjectionable noise emission, one at the inlet end of the engine nacellewhere the high speed shearing effect of the fan and stator blades on theinrushing inlet air produces a high pitched siren effect, and the otherat the exhaust end where the high velocity exhaust gases have their.shearing encounter with the ambient atmosphere.

It is well known that the amount of objectionable noise emanating fromthe intake end of a jet engine can be attenuated by increasing theinternal surface area available for acoustical treatment, and it is notbroadly new to mount one or more annular airfoil type members, calledsplitter rings, co-axially within the intake duct. However, such ringspresent serious problems in that they must be rigidly and stronglymounted, with no danger of any portion thereof coming loose to beswallowed by the engine, while at'the same time they should be easilyremovable, either in whole or in part, for inspection, maintenance orreplacement.

SUMMARYVOF THE INVENTION It is a principal objective of this inventionto mount one or more streamlined, sound absorptive, inlet air dividerrings coaxially within the air inlet duct of a jet engine, the ring orrings being assembled in removable panel segments supported by radiallyextending struts.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objectives andadvantages of the invention will be apparent from the followingdescription and theaccompanying drawings, wherein:

FIG. 1 is fragmentary, front, elevational view of-approximately onequarter of a two ring assembly embodying one form of the invention as itappears when looking into the up stream end of the intake duct of anengine nacelle in which the rings are mounted, the nacelle cowling beingremoved, the inner face of the cowling and the nose cone being indicatedin broken lines.

FIG. 2 is a sectional view taken along offset line 2--2 of ,FIG. 1.

FIGS. 2A and 2B are fragmentary, enlarged sectional views through thetrailing and leading end portions, respectively of one of the splitterrings.

FIG. 3 is an enlarged, fragmentary, sectional view taken along line 3-3of FIG. 2, portions being broken away to show the piano hinge typeconnection between the honeycomb panels and the longerons.

FIG. 4 is a further enlarged, fragmentary, sectional view taken alongline 4-4 of FIG. 3.

FIG. 5 is a fragmentary, longitudinal sectional view on a radial planethrough one side of the annular air inlet passage of an airplane jetengine pod having a modified form of the invention embodied therein.

FIG. 6 is a fragmentary plan view of the radially inward side of FIG. 5,which is the top side as shown in FIG. 5, a portion being broken away.

FIG. 7 is a sectional view taken along line 77 of FIG. 5.

DETAILED DESCRIPTION Referring to the drawings in detail, andconsidering first the form of the invention shown in FIGS. 1-4, theinlet duct A of a conventional jet engine nacelle is defined by a hatsection reinforcing band 10, see FIG. 2, encircling a conventionalcowling structure 1 l.

A plurality of five identical struts 12 of streamlined, longitudinalsectional shape are mounted in the inlet duct A along symmetricallyangularly spaced radial planes from the inlet duct axis 13. Each strut12 has a mounting plate 14 on its radially outward end secured to thecowling 11 by removable fasteners 15. Each strut 12 is hollow, and maybe of drawn or extruded metal, or formed from suitable sheet metal suchas stainless steel, titanium, or aluminum alloy. The struts 12, as shownin FIG. 2, are raked back toward their inner ends approximately 25 froma radius from the inlet duct axis.

Two longerons l7 and 18 are mounted on each strut 12, one longeron 17being mounted on the radially inward end of the strut, and the other 18at a desired or designed intermediate location. The longerons, like theair divider rings B and C of which they constitute narrow segments, areshaped in longitudinal section to conform to the normal flow of inletair through the inlet duct A. Since both air divider rings B and C aregenerally similar to each other only the structural details of the innerring B will be described in detail herein.

Each longeron 17 is of generally inverted T" cross sectional shape asshown in FIG. 4, and has a strut receiving hole 19 therethrough, seeFIGS. 3 and 4, shaped to receive the strut 12 in fitted relationtherein. Each strut 12 is inserted a required distance in each of itstwo longerons 17 and 18 as shown in FIG. 2, and the longerons are weldedto the strut around the top and bottom of each strut-receiving openingin each longeron.

An elongated opening 20, see FIGS. 2 and 4, is provided in each side ofeach longeron to open into the hollow interior of the struts mountedtherein, and matching opening 21, see FIG.

4, is provided in each side of each strut to register with theseopenings 20 in the longerons when the longerons are mounted on thestrut. The openings thus provided into the hollow interior of each strutprovide a path for anti-icing air.

A plurality of transversely curved, segmental, honeycomb panels 22 arefitted in complementary relation between the longerons 17, so that thecomplemental segments defined by the longerons 17 and panels 22 form theair divider ring B;

Each panel 22, as best shown in FIGS. 3 and 4, comprises two layers 23and 24 of honeycomb core material in back-toback relation on oppositesides of a common intermediate or backing .layer 25, and a pair of facesheets 27 and 28, spaced from the backing sheet 25 by the honeycombcores 23 and 24, respectively, to provide resonant cavities between theface sheets and the backing sheet. The two face sheets 27 and 28 are oflight gauge metal, and have a multiplicity of small holes 29therethrough, see FIG. 3, in an overall pattern in accordance withcommon practice for this type of sound absorptive material. Usualdoubler strips 30 are provided along exposed marginal areas of the facesheets 27 and 28 for reinforcing. The face sheets 27 and 28, doublerstrips 30, honeycomb cores 23 and 24 and the central backing sheet 25are secured together in closely superposed relation as shown in FIGS. 2and 4 by conventional means, such as brazing. Distinguishing thestructure of the panels 22 from usual practice is the thickness of thecentral backing sheet 25, which is of relatively thick, structural sheetmaterial.

For mounting the panels 25 between adjacent longerons 17, each panel 25has two half portions 31 and 31a, see FIGS. 3 and 4, of a piano hingetype member firmly secured, by rivets 32 or other suitable means, suchas bonding or brazing, one to each lateraledge thereof. Thecomplementary half portions 33 and 33a of said piano hinge type membersare secured, respectively, by machine screws 34 to the lateral offset orhead portions 35 and 35a of each inverted T-shaped longeron 17. A shimstrip 35 of selected thickness is interposed between each longeron hingehalf portion 33 and 33a and its associated longeron 17 to bring the facesheets of the panel flush with the faces of the longeron laterallyadjacent thereto. The outer face sheet 28 of each panel 22 and itsdoubler strip 30 extends beyond the core 24 a sufficient distance tosubstantially close the gap between the face sheets 28 and the stemportion of the inverted T-shaped longeron 17. The abutments of the pianohinge type half portions 33 and 33a of each longeron 17 are sopositioned, relative to the abutments on the piano hinge type halfportions on the panels 22 to which they areconnected as to fittherebetween in relatively interdigitated relation, with the hinge pinholes in both sets of abutments in substantial alignment with each otherto receive a hingepin 45 to securedly attach the panels in complementaryrelation between the respective longerons.

Streamlined terminal fairings 40 and 41 are provided on the upstream anddownstream ends, respectively, of both air divider rings Band C. Thenose fairing 40 for the upstream or leading edge of the ring B comprisesa plurality of longeron nose portions 40a, and panel nose portions 40b.

Each longeron nose portion 40b, see FIGS. 3 and 6, is of the same widthas the base of the longeron 17 upon which it is mounted, and is roundedat its leading end 42, see FIG. 6. The downstream end of each longeronnose fairing 40b is fitted into a notch 43, see FIG. 6, providedtherefore in the upstream end of its associated longeron 17, and isconnected thereto by screws 44. Each longeron nose fairing 40b fitsflush with the outer surfaces of its respective longeron.

A panel nose fairing 40a, generally similar in longitudinal section tothe longeron nose fairing 40b, is secured in a notch provided thereforin the leading edge of each panel.

Tail fairings 41a and 41b are similarly mounted in the downstream end ofeach longeron 17 and panel 22, the downstream end of each tail fairingterminating in a usual edge 47. The nose and tail fairings in thelongerons 17 and OPERATION The air divider ring assembly shown in FIGS.1-4, comprising the five struts 12 with their two sets of longerons l7and 18, and two sets of complementary, interfitted panels 22 and 26,with their nose and tail fairings mounted thereon, is mounted co-axiallyin the inlet air duct A of a jet engine nacelle, and is fixedly securedtherein by the rivets 32 or other suitable mounting means. Anyinstrumentation required is usually accomplished before assembly andinstallation, and the instrument wires are brought into one or moreselected struts 12 through aligned openings 20 and 21, and thenceoutwardly through the outer ends of the struts.

In the event that maintenance or inspection subsequently requires theremoval of one or more of the panels 22 or 26, the longeron nosefairings 40b or the tail fairings 41b, or both, of the longerons on eachside of each such panel are removed, and the hinge pins 45 arewithdrawn, thereby freeing the panel or panels for removal. The panel orpanels, or replacements therefor, are replaced by reversing theforegoing procedure.

MODIFIED FORM OF INVENTIONS FIGS 5 7 Referring now to the form of theinvention shown in FIGS. 5-7, the forward end portion of a conventionalcowling 50 defining the annular air inlet duct 51 for an aircraft jetengine, not shown, has an inner wall 53 of suitable sound absorptivematerial, for example, formed, acoustical, honeycomb sandwich panelmaterial of a well known type referred to previously herein. The usualaxial nose cone 54 also preferably is. faced with acoustical honeycombcore sandwich or other sound absorptive material in accordance withcommon practice where sound suppression is required.

A plurality of splitter ring panel stowage pockets 55 are formed in thecowling inner wall 53, and a panel set 57 which consists, in the presentinstance, of three splitter ring panels 58, 59 and 60 and a closurepanel 61, are housed in each of said pockets.

Each pocket 55 extends lengthwise of the inlet duct 51 and its size andshape are determined by the innermost panel 58 of a panel set 57 to behoused therein. The pockets 55 are distributed symmetrically about theaxis of the inlet duct.

As used herein inner, inwar and words of similar connotation mean towardthe inlet duct axis," while outer," outward,"etc. mean the reverse.

In their retracted position the panels of each set are housed in theirrespective pockets 55 with the inner panel 58 flushmounted in fittedrelation in an opening 62 in the cowling inner wall 53, which openingcomprises the opening of the pocket. The surface configuration of eachinner panel 58 is such as to complement and conform substantially tothat of the cowling inner wall 53 when the panels are retracted tostowed position in their respective pockets 55 as shown in broken linesin FIG. 7.

Each innermost panel 58 has an elongated, streamlined strut wall 63, ofacoustical honeycomb sandwich panel material integrally mounted on theradially outward side thereof, and this strut wall fits for freetelescopic movement within a similar, but larger strut wall 64 formed oneach intermediate splitter panel 59. Each panel 59 is substantiallysimilar in shape, size and surface configuration to the innermost panel58, with the exception that the intermediate panel has an opening 66therein to receive the strut wall 63 of the innermost panel 58 therein.

The third splitter ring panel 60 of each set in turn is generallysimilar in size, shape and surface conformation to the intermediatepanel 59 and has a streamline strut wall 65 thereon, and an opening 67therein to receive the strut wall 64 of the intermediate panel 59telescopically therein. Additionally, an outer closure panel 61 issecured near the lower end of the strut wall 65 of each third splitterpanel 60, and is of a size, shape and surface conformation, and is somounted on its strut wall 65, that when the panels are deployed as shownin FIG. 5 and in solid lines in FIG. 7, each outer closure panel 61 fitsinto and closes its respective pocket opening 62 in the inner cowlingwall 53.

For guiding and supporting the panels of each set during deployment andretraction, a pair of telescoping guide tube assemblies and 76 areprovided. Since the two sets of telescoping tubes are similar, only theforward one 75 is described in detail. A fixed stud 77 is secured to theouter wall 74 of the cowling 50, and a fixed tube 69 is fixedly securedthereon. A first telescoping tube section 79, is mounted in relativelytelescoping relation on the fixed tube section 69, and other telescopingtube sections 80 and 81 are mounted in successive telescoping relationon the tubesection 79, the final tube section 81 being fixedly securedat its upper end to the innermost panel 58.

A stop pin 82 is provided near the top of the fixed tube 69, and ridesin a slot 83 provided in the tube 79 to limit axial separative,telescoping movement of the tube 79. Similar pins and slots are providedfor the other telescoping tubes 80 and 81. Also, pins 84 riding in slots85 provided in the strut walls limit the telescopic projection of thestrut walls in a similar manner to position the panels of each set intheir deployed position.

It will be apparent that more positiveacting and sophisticated mechanismwill probably be preferred for guiding the panels between their deployedand stowed positions, but such mechanism is not a feature of the presentinvention, and will be designed in accordance with the requirements ofeach type of installation in which the invention is to be embodied.

For actuating the panels of each set 57 between their stowed andactuated positions, a pair of actuator links and 91 are pivotallyinterconnected at 92. The inner link 90 is also pivotally connected at93 to the innermost panel 58, and at 94 to the outer cowling wall 78.Link actuating means comprises a hydraulic or pneumatic cylinder 95pivotally mounted on a standard 97 secured to the cowling outer wall 78.The piston rod 98 of the cylinder 95 is pivotally connected to the linkjoin 92, and actuation of the cylinder 95 moves the links between theirsolid and broken line positions of FIG. 5 to move the panels betweentheir deployed, solid line position of FIGS. 5 and 7, and their stowed,broken line position of FIG. 7.

Each innermost panel 58 is so shaped, and its position upon deploymentis so calculated, that in their deployed, solid line positionshown inFIG. 5 and in solid lines in FIG. 7, these inner panels aresubstantially in lateral edge-to-edge, supplemental relation as shown inFIG. 7 to form a complete, but not quite circular splitter ring.

The other splitter panels 59 and 60 of each set are spaced laterallyedgewise from each other, even when deployed, as is shown in FIG. 7, andthus comprise segments defining additional sound absorptive splitterrings having gaps or spaces between adjacent panels.

The outer closure panels 61, being integrally secured to theirrespective strut walls 65, are elevated upon deployment of theirrespective panels 60, to fit into and close the pocket opening 62 in theinner cowling wall 53, in which position they conform to the curvatureof said inner wall. All of the panels are formed lengthwise to conformto the normal flow of inlet air thereover during operation of the engineso as to minimize stresses on the panels as well as interference withair flow through the inlet duct.

OPERATION OF FORM OF FIGS. 5-7

In the form of the invention shown in FIGS. 5-7, with the piston rod 98extended as shown in broken lines in FIG. 5, the panels 58, 59, 60 and61 of each panel set 57 are retracted to stowed position as shown inbroken lines in FIG. 7, in which position the stop pins 82 and 84 are atthe radially inward ends of their respective slots, and the radiallyinnermost panel 58 is fitted into the opening 62 in the cowling innerwall 53 and the air inlet duct 51 is thus entirely clear andunobstructed. This stowed condition of the panels provides maximumefficiency for flight beyond the environs of an airport, where noiseemission is not a serious problem.

For landing approach and takeoff, where maximum sound absorption isrequired, the cylinder 95 is actuated to retract the piston rod 98 andthereby extend the links 90 and 91 to their solid line position of FIG.5. This extends the telescopically interfitted strut walls 63, 64 and 65and the telescopic tubes 75 and 76 to their deployed position shown inFIG. 5 and in solid lines in FIG. 7. Engagement of the stop pins 82 and84 with the radially outward ends of their respective slots limits theradially inward deployment of their respective panels to their designed,deployed positions.

In their deployed positions both sides of each of the panels 58, 59 and60, as well as the outer face of the outer closure panels 61 absorbsonic energy in a well known manner as do also the strut walls 63, 64and 65 while at the same time the panels 58, 59 and 60 tend to smoothenthe flow of inlet air through the inlet duct 51 and into the usualcompressor turblue, not shown, of the engine upon which the air inletduct 51 is mounted. Such smoothening of the inlet air flow reducesturbulence, which, at high velocities, itself tends to generate noise.

The invention provides a strong, safe, rigid, annular air divider orsplitter ring structure which adds substantially to the area availablewithin the inlet duct for sound absorptive treatment, and does notsubstantially adversely affect either engine performance or drag.

Having described my invention, what I now claim and desire to protect byLetters Patent of the United States of America is:

1. Sound suppression mechanism for an aircraft jet engine having a cowlwith an annular inner wall defining an air inlet duct co-axially of andforwardly of the engine, said mechanism comprising:

a plurality of panel receiving pockets formed in symmetrically,circumferentially spaced relation in the cowl inner wall,

a set of splitter ring panels of a size and shape to fit, in relativelysuperposed, stowed relation, into each pocket,

extensible strut means mounted in each pocket and operatively connectedto the panels in each pocket, each strut means being extensible fromstowed position, with the panels of its respective set stowed in theirrespective pocket, to extended position with correspondin panels of eachset deployed at equally spaced intervals rom the cowling, and co-axiallyof the air inlet duct, whereby the corresponding panels of each setdefine an annulus coaxial with each other and with the air inlet duct.

2. Sound suppression mechanism as defined in claim 1 wherein theinnermost panel of each set is of a size and shape to have lateral,edgewise, contacting relation with the lateral edges of the innermostpanels on both sides thereof with the panels in deployed position.

3. Sound suppression mechanism as claimed in claim I wherein the panelsof each set comprise at least an inner splitter ring panel shaped to fitinto and to close the opening into its respective pocket with the panelsin their stowed position, and an outer closure panel shaped to fit intoand to close the opening into the pocket with the panels in theirdeployed position.

4. Sound suppression mechanism as defined in claim 3 wherein at leastone splitter ring panel is provided intermediately of each inner paneland its respective outer closure panel, and the outer closure panel isfixedly connected in spaced relation to such intermediate panel.

* it i

1. Sound suppression mechanism for an aircraft jet engine having a cowlwith an annular inner wall defining an air inlet duct coaxially of andforwardly of the engine, said mechanism comprising: a plurality of panelreceiving pockets formed in symmetrically, circumferentially spacedrelation in the cowl inner wall, a set of splitter ring panels of a sizeand shape to fit, in relatively superposed, stowed relation, into eachpocket, extensible strut means mounted in each pocket and operativelyconnected to the panels in each pocket, each strut means beingextensible from stowed position, with the panels of its respective setstowed in their respective pocket, to extended position withcorresponding panels of each set deployed at equally spaced intervalsfrom the cowling, and co-axially of the air inlet duct, whereby thecorresponding panels of each set define an annulus co-axial with eachother and with the air inlet duct.
 2. Sound suppression mechanism asdefined in claim 1 wherein the innermost panel of each set is of a sizeand shape to have lateral, edgewise, contacting relation with thelateral edges of the innermost panels on both sides thereof with thepanels in deployed position.
 3. Sound suppression mechanism as claimedin claim 1 wherein the panels of each set comprise at least an innersplitter ring panel shaped to fit into and to close the opening into itsrespective pocket with the panels in their stowed position, and an outerclosure panel shaped to fit into and to close the opening into thepocket with the panels in their deployed position.
 4. Sound suppressionmechanism as defined in claim 3 wherein at least one splitter ring panelis provided intermediately of each inner panel and its respective outerclosure panel, and the outer closure panel is fixedly connected inspaced relation to such intermediate panel.